解放军文职考试：过去完成时经典例题

We won"t know how the plan works till we have tried it ________.
答案 :
out　
They__________on the program for almost one week before I joined them, and now we ________on it as no good results have come out so far.

A．had been working; are still working	B．had worked; were still working
C．have been working; have worked	D．have worked; are still working

答案 :
A